arXiv subjects

Anooj Thayyil Raveendran

Publications and source records attributed to Anooj Thayyil Raveendran.

3 recordsLinked to original sources

arXiv2026

Multi-contrast wide-field mid-infrared photothermal imaging

Wide-field mid-infrared photothermal (MIP) imaging enables high-speed, chemically specific imaging at sub-micrometer spatial resolution through several possible contrast mechanisms, including scattering change, fluorescence modulation, and phase change. Each mechanism offers distinct advantages, yet existing wide-field MIP instruments have typically been limited to a single contrast mechanism so far, requiring a dedicated instrument for each. Here, we introduce a switchable multi-contrast wide-field MIP microscope that allows the photothermal readout mechanism (based on scattering-, fluorescence-, or quantitative phase imaging (QPI)) to be matched to the sample and imaging conditions. We characterize the spectral fidelity and signal-to-noise (SNR) ratio of each mechanism using 5 μm polystyrene (PS) beads, and the effective spatial resolution using 300 nm PS beads. Scattering- and fluorescence-based detection achieved a sub-500 nm measured point spread function full width at half maximum, while QPI-based detection reached approximately 900 nm but provided up to 26-fold higher SNR than scattering. We further demonstrate imaging across a range of samples, including A549 cells in buffer, mouse lung tissue section, bacteria, and SU8 polymer at 1.4 and 5 μm thickness, with a field of view exceeding 200 μm. Comparison across these samples shows that each contrast mechanism offers distinct trade-offs in resolution, sensitivity, and applicability, guiding readout-strategy selection by sample type. These results establish a flexible, switchable multi-contrast platform for wide-field MIP imaging, with broad applicability across polymer and biological samples.

physics.optics↗

arXiv2026

Millimeter-scale wide-field mid-infrared photothermal imaging enabled by a broadly tunable picosecond optical parametric oscillator

Wide-field mid-infrared photothermal (MIP) imaging enables chemically specific microscopy with submicron spatial resolution but remains fundamentally limited by the trade-off between field of view, mid-infrared pulse energy, and spectral tunability. As a result, current wide-field implementations are typically restricted to fields of view below 200 μm and to either the fingerprint or high-wavenumber spectral regions. Here, we overcome these limitations by developing a wide-field fluorescence-detected mid-infrared photothermal (F-MIP) imaging platform driven by a commercial picosecond optical parametric oscillator (OPO). The system provides pulse energies of up to 360 μJ together with a broad tuning range from 625 to 4327 cm-1, enabling millimeter-scale wide-field imaging in the high-wavenumber regions. We demonstrate a field of view of approximately 1 mm in diameter for fluorescently labeled polystyrene beads while preserving spectral fidelity. Furthermore, the platform enables, to our knowledge, the first wide-field MIP imaging below 900 cm-1. To demonstrate its applicability to biomedical imaging, we performed large-area mosaic imaging of fluorescent tuberculosis-infected tissue sections, providing chemically resolved maps over millimeter-sized sample areas. These results establish broadly tunable OPO-driven F-MIP as a scalable platform for high-throughput vibrational imaging of large biological specimens and advanced materials.

physics.optics↗

arXiv2026

Free-electron laser-based extended wide-field mid-infrared photothermal imaging for biomedical and microplastic analysis

Wide-field mid-infrared photothermal (MIP) imaging offers rapid labelfree chemical contrast for biomedical and polymer analysis. However, its field of view (FOV) is limited by the pulse intensity of conventional infrared lasers. Here, we present a wide-field MIP microscope that uses a high-power free-electron laser (FEL) rather than a quantum cascade laser (QCL) as the pump source to achieve a substantially larger FOV. Both implementations use counter-propagating beam paths with a 450 nm LED as the probe source and a CMOS camera that records images using a virtual lock-in detection scheme. QCL nanojoule pulse energies enables FOV of around 45 micrometers for widefield MIP imaging with a sub-micrometer resolution for polystyrene beads, Mycobacterium tuberculosis infected fixed tissues, and laryngeal cancer cryosections. IR spectra in the range of 1000-1800 wavenumbers can be reconstructed by tuning the QCL. FEL pulse energies of up to microjoules expand the FOV by a factor of nearly 20 as demonstrated by wide-field MIP imaging of polystyrene beads, single cells, and murine brain tissue. We discuss current challenges and further improvements to implement high-power IR lasers for wide-field MIP imaging with even larger FOVs in the context of biomedical research and diagnostics.

physics.optics↗